All the above scenarios have been economically evaluated and
compared using general profitability criteria [40]. The most
significant is the Net Present Value (NPV), which gives the profit of
the plant for a certain period by considering the time value of
money. Other criteria such as return on investment (ROI),
discounted payback period (DPBP), payback period (PBP), internal
rate of return (IRR) and gross margin are also calculated. To evaluate
the profitability of the different schemes we have set the lifetime of
the plant to 20 years. We have assumed that the construction of the
plant finishes at the end of the first year and it starts to operate at
its maximum capacity straight ahead. Working capital and land
value are not included as well as any salvage value of the plant at
the end of the lifetime. The rate of interest (i) used in this study set
to be 7% and no taxes are charged against the plant’s profits
assuming a tax support system for biofuels.